1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, in which both a high-breakdown-voltage MOS (Metal Oxide Semiconductor) transistor and a low-breakdown-voltage MOS transistor having different drain breakdown voltages are formed on an identical substrate, and also to a semiconductor device manufactured by this method.
2. Description of the Related Art
An integrated circuit for actuating, for example, an imaging element, an LCD, or a print head (hereinafter referred to as the ‘actuation IC’) generally includes an actuation output module with a high-breakdown-voltage MOS transistor, which is driven by a power supply voltage of 10 or greater volts and has a high withstanding breakdown voltage between a drain and a source (hereinafter may be referred to as the ‘drain breakdown voltage’), and a logic module with a low-breakdown-voltage MOS transistor, which is driven by a power supply voltage of several or less volts and has a low drain breakdown voltage, for controlling the actuation output module. In the description below, the MOS transistor may be simply called the transistor.
In the actuation IC, it is preferable that the high-breakdown-voltage transistor and the low-breakdown-voltage transistor are formed on an identical substrate. The simplest method of forming such transistors of different withstanding breakdown voltages on an identical substrate is to separately form the respective transistors according to different processes. The method first forms one of the high-breakdown-voltage transistor and the low-breakdown-voltage transistor on a substrate, and subsequently forms the other transistor on the same substrate.
The method of separately forming the high-breakdown-voltage transistor and the low-breakdown-voltage transistor, however, significantly increases the total number of manufacturing steps, thus worsening the production efficiency and increasing the manufacturing cost.
There is accordingly a demand for efficiently forming a high-breakdown-voltage transistor and a low-breakdown-voltage transistor on an identical substrate without damaging the characteristics of the respective transistors.